Friday, January 20, 2017

Pixel Art Upscaling Test Image

At the RetroArch/libretro forums, we get a lot of requests for shader previews because there are a lot of them and many people--particularly new users--get overwhelmed and don't know where to even start. So, we've batted around the idea for a while but there were some complications, namely that it's hard to get a good representative preview without managing giant, full-res images, and it's difficult to show of the effects of some shaders while still making the previews directly comparable to one another.

To handle these issues, I decided to make a small test image that contains many of the important features for a retro-focused upscaling algorithm to handle (this is enlarged; it's actually 64x64):

It was a fun exercise trying to pack as many tests as possible into this small canvas. There are two gradients--red-to-green and black-to-white--to test banding, several styles of text, some space invaders to test effects on isolated pixels surrounded by another color, the blended/antialiased doom-guy head, a variety of slopes that go from 1:1 up to 6 pixels of run to a single pixel of rise, the pesky circle-C copyright symbol, some parallel lines and a checkerboard to test de/dithering response/false-positives and a multicolored square that turns into a green-and-beige checkerboard in the presence of NTSC signal modeling, like this:

For the preview repo, I ran the test image through each shader preset at 8x integer scale (or slightly above that for the sharp-antialiased shaders). I don't have previews available for all of the presets yet at the time of this writing, but most of the popular ones are covered. These previews will hopefully make their way into RetroArch at some point, but in the meantime you can browse them at the repo.